This application claims priority from Korean Patent Application No. 2002-68367, filed Nov. 6, 2002, the content of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a head-mounted display (HMD) designed to view video images when mounted on a user""s head, and more particularly, to a head-mounted display using retinal direction projection, which has a small and lightweight structure by changing the configuration of optical elements and optical arrangement.
2. Description of the Related Art
In general, head-mounted displays (HMDs) appear in the form of eyeglasses or helmets. A HMD is a personal see-through device designed to view video images only when a user wears it. The HMD may use a magnifier, an optical relay lens, or retinal direct projection technology depending on the optical system configuration.
While a magnifier approach can produce a virtual image with a large field of view through a very small magnifier lens, it increases eye fatigue. A HMD using a relay lens reduces eye fatigue because a viewer can observe an image displayed on the screen from a distant position, but its size is too large for helmets. A retinal direct projection technique that has an image displayed on the screen directly projected onto the retina not only reduces eye fatigue but also makes the size of a display smaller than when the relay lens is used.
FIG. 1 shows a conventional HMD using retinal direct projection technology disclosed in Japanese Patent Laid-Open Publication No. Hei 3-214872 (Sep. 20, 1991).
Referring to FIG. 1, the conventional HMD includes a point light source 1 consisting of a tungsten lamp, a condensing lens 2 for condensing light emitted from the point light source 1, a plurality of reflecting mirrors 3 and 4 for converting the path of incident light, eyepieces 5, 7, and 8 consisting of three element lenses, and an image plate 6 positioned between the eyepieces 5 and 7 for producing an image by selectively transmitting the incident light. This HMD device focuses the image irradiated from the point light source 1 and produced by passing through the transmissive image plate 6 at the focal point of an eyeball 9.
However, as described above, the conventional HMD is not of small size and lightweight structure because it requires a plurality of optical components such as condensing lens 2, reflecting mirrors 3 and 4, and eyepiece 5 between the point light source 1 and image plate 6.
The present invention provides a small, lightweight head-mounted display by changing the configuration of optical components and optical arrangement.
According to the present invention, there is provided a head-mounted display including: a planar backlight for producing and emitting planar light; a light-speed controlling element disposed in front of the planar backlight for controlling the speed of incident light so that the light propagates parallel or near parallel to an optical axis; an image-forming element disposed in front of the light-speed controlling element for forming an image; and a Fresnel lens disposed in front of the image-forming element for focusing the incident image onto an eyeball.